In related arts, a screw may include a right-handed screw and a left-handed screw. The right-handed screw may include a thread groove or a thread in a form of a right-handed helix, and the left-handed screw may include a thread groove or a thread in a form of a left-handed helix. A screw formed on a periphery surface of a cylindrical hole in a solid member provided in, for example, a hexagonal prism, is referred to as an internally-threaded screw or a nut. A threaded body including a screw formed on an outer peripheral surface of a cylindrical member is referred to as an externally-threaded screw or a bolt. The externally-threaded screw and the internally-threaded screw may be screwed together for use.
An internally-threaded body with a right-handed screw may be paired with an externally-threaded body with a right-handed screw for use, and an internally-threaded body with a left-handed screw may be paired with an externally-threaded body with a left-handed screw for use. However, it is impossible to screw the externally-threaded body with the right-handed screw with the internally-threaded body with the left-handed screw. Conversely, it is impossible to screw the externally-threaded body with the left-handed screw with the internally-threaded body with the right-handed screw.
Accordingly, there is a desire for technology that may distinguish between a right-handed screw and a left-handed screw in an internally-threaded body to suitably screw an externally-threaded body with a left-handed screw or a right-handed screw paired therewith. The reverse may also be applied to the externally-threaded body. However, in related arts, a threaded body, particularly an internally-threaded body or a nut may include a thread portion on an inner peripheral surface thereof. Thus, there may be no difference in terms of an external appearance or an outer surface, and it may be impossible to rationally distinguish between a right-handed screw and a left-handed screw based on an external appearance or an outer surface of the internally-threaded body.